The invention relates to a magnetic resonance method for forming a fast dynamic image from a plurality of signals from an RF probe according to the preamble of claim 1. The invention also relates to a magnetic resonance imaging apparatus for obtaining a fast dynamic image according to the preamble of claim 1 and to a computer program product according to the preamble of claim 6.
In U.S. Pat. No. 5,928,148 data is acquired from a large region of interest in magnetic resonance angiography (MRA) by translating the patient to successive stations at which successive portions of the MRA data set are acquired. The patient is moved to three successive locations between the RF coils of the MRI system by translation of the patient table. The patient movement is chosen to track a bolus of contrast agent as it passes through the region of interest so as to achieve maximum image contrast. In one embodiment a stationary local coil is supported adjacent the patient to acquire the MRA data and in another embodiment a multi-segment local coil moves with the patient and its segments are sequentially switched into operation.
In a further patent application of the same inventors, that is, WO-A-99/27382 which concerns a further development of the same acquisition method, it is mentioned that the successive acquisition at each Field of View (FOV) may not be fast enough to track with the bolus of contrast agent as it passes through successive FOVs. For example, it may require nearly 50 seconds to acquire 3D NMR data from three FOVs, and the contrast may be at peak level for only 30 seconds. Therefore, it is proposed that sampling orders for each FOV acquisition be selected to sample the central region of k-space when the contrast is at its peak value. This means that data will be sampled along lines in k-space that are directed towards the central part. The drawbacks of sampling in the peripheral views of k-space which are not at peak value are thus compensated to a great extent.
Since the coil or coils used for the acquisition of the MRA data are at a fixed position with reference to the patient and the dimensions of the coil or coils are in the range of at least from 10 to 20 cm length and width, the spatial resolution of the image formed from the combination of successive FOVs will be reduced. On the other hand there may be aberrations and artefacts in vertical directions if a proper three-dimensional image is acquired. As is further indicated in the latter document, the sampling time may be too long in order to track a faster moving probe.
It is an object of the present invention to provide a method for forming a fast dynamic image of a moving RF probe which can be optimally tracked without any delay. Another object of the present invention is to provide a magnetic resonance apparatus for obtaining a fast dynamic image of a moving RF probe.
An essential advantage of the method for forming a fast dynamic image according to the present invention is that on the one hand an MR image over a combination of several FOVs with a high resolution can be obtained while on the other hand a bolus can be tracked along a vessel in real time without any delay. So depending on the aim, a high spatial resolution or a high temporal resolution can be achieved.
These and other objects of the invention are achieved by a method as defined in claim 1, by an apparatus as defined in claim 5 and by a computer program product as defined in claim 6.